A tuned damped absorber arrangement is used to attenuate the response of an encoder. If a vibration disturbance is of a high amplitude and/or if processing conditions result in a resonant condition, the encoder can lose its position. Excessive vibration can also damage the internal electronic components of the encoder.
The vibration problem occurs on rotary axis heads which are used in machining operations. When using long slender tools, a vibration can be created which causes the encoder to lose its position.
Encoders by their nature should not be isolated from the axis which they are controlling since to do so would potentially result in a loss of position indicating accuracy. The device relies on the use of a tuned damped absorber in a unique configuration for its operation. The device exhibits a significant attenuation of unwanted vibrations that are both lateral and torsional. The improved response eliminates the lost axis position situation and improves the reliability and life of the encoder.
In one application, the mounting of the encoder on a fairly slender beam exacerbates the problem of resonant vibration. The damper device addresses the vibration exhibited at the encoder under both an unbalanced response and during cutting operations. One embodiment addresses torsional response, another addresses the lateral response of the beam to which the rotating part of the encoder is mounted.
It is believed that tool vibration is exciting the encoder during chatter and causing mechanical noise on the encoder output signals. If the vibration that normally affects the encoder can be attenuated by a damper without affecting other aspects of velocity loop bandwidth, the damper should eliminate the problem.
The vibration problem has appeared typically in cutting applications of aluminum at a fairly high speed and is often more prevalent when the cut results in tool chatter. In one application, a long slender tool is used with resulting chatter that is approximately equal to the torsional mode of the input shaft of the encoder. The chatter has been known to cause the rotary axis of the encoder to drift, thus giving an incorrect reading.
When chatter occurs, the A-axis position of the encoder drifts. Vibration of the input shaft of the encoder is the likely root cause of the drift. It is believed that the chatter frequency is in the 1000 to 2000 Hz region for tool modes.